MEMS chips (micro electromechanical systems) combine electronic elements and micromechanical structures on a semiconductor chip and can process electrical and mechanical information. They are deployed in sensors, actuators and other items.
In the operating state the measuring regions of the MEMS chips of the above-described type are exposed to the pressure space, whereby appropriate measured signals that are recorded in the pressure space can be taken off the contacts. Such MEMS chips are suitable for a pressure-tight arrangement in a bushing, which can be formed by a full peripheral encasement of the surface of the bushing region 11 normal to the longitudinal axis A.
Embodiments of such MEMS chips of known art are, for example, described in WO 2004/081510 A1, or also in the publication of Birkelund K et al: “High pressure silicon sensor with low-cost packaging”, SENSORS AND ACTUATORS A, ELSEVIER SEQUOIA S. A., LAUSANNE, SWITZERLAND, Vol. 92, No. 1-3, Pages 16-22. Such MEMS chips have in the measuring region a cavity in the carrier substrate, which is closed by a silicon-on-insulator (SOI) wafer, whereby a measuring bridge is fitted within the cavity on the SOI wafer. Moreover, in the whole of the forward region of the MEMS chip the SOI wafer is configured with a reduced thickness, so that the latter operates there as a membrane.
The stiffness of this membrane, which is responsible for the sensitivity of the MEMS chip, or more particularly the measuring element, is now adjusted via the remaining residual thickness of the SOI wafer in the measuring region. This is relatively costly, since the thickness reduction as a rule is achieved by selective etching of the silicon layer: the longer the etching process, the thinner becomes the membrane layer. However, since these etching times are very short, an accurate reproduction of a specified membrane stiffness becomes extremely difficult.